Filtration barrier

ABSTRACT

A filtration barrier includes a filter mesh that has a plurality of groups of flexible filter elements, with each group having at least a first and second flexible filter elements disposed in spaced relation. The first flexible filter element is more flexible than the second. Each flexible filter element is secured to the first and second anchoring members of the mesh and free therebetween. During forward fluid flow, the first and second flexible filter elements are supported against downstream deflection and lie in a common plane. For reverse fluid flow, the first flexible element of a group displaces farther from the common plane than the second flexible filter element of that group, such that a first backwash opening associated with the first flexible element is larger than a second backwash opening associated with the second flexible element. Each group may have more elements, and associated methods are also disclosed.

This application is a divisional of U.S. patent application Ser. No.12/934,787, filed 27 Sep. 2010, which is a National Stage entry ofPCT/AU2009/000401, filed 2 Apr. 2009, which claims benefit of AustralianApplication 2008901762, filed 11 Apr. 2008, the disclosures of all ofwhich are incorporated by reference herein in their entirety.

BACKGROUND

The invention relates to filters wherein the elements forming thefiltration apertures enlarge during reversals of the filtrate flow.

Filtration barriers, particularly filter screens and meshes, require aperiodic reversal of the fluid flow through the barrier (termed aback-wash) to clear the barrier of captured and entrapped solidparticles. The back-washed filtration barrier is then ready for afurther filtration. Attention is directed to WO 98/23357 (Obst).

SUMMARY

The invention provides in a first aspect a filtration barrier comprisinga plurality of apertures that permit passage of a fluid, but restrictthe passage of particles of sizes greater than the aperture width. Theapertures are first spaces between neighboring bristles or elements. Aplurality of bristles or elements are securely attached to a singlesupport bar to form a comb. Each bristle or element has a free end withits other end attached to the single support bar with all bristles orelements arranged parallel to each other. The plurality of said combsare arranged with second spaces between each pair of adjacent singlesupport bars in a parallel array so that the free ends of the bristlesor elements of each comb of the plurality of combs overlap the supportbar of the next comb in the array. The bristles or elements of each combbranch from the support bar and lie in a common plane in their relaxedstate. Each support bar is supported upon a plurality of support joistsarranged transversely to the support bars. Each bristle or element issupported at its free end by the next comb, and each bristle or elementis of a stiffness and length that permits each bristle or element toyield only slightly under pressure from fluid flowing forwardly betweenthe bristles or elements towards the support joists. When fluid flowsbackwardly through the barrier each bristle or element is unsupported atits free end, whereby the bristles or elements yield under pressure fromthe backwardly flowing fluid and the free ends of bristles or elementsare raised above the next comb, or combs, thereby enlarging the flowarea through the filter barrier, and imparting a tangential direction tothe fluid leaving each comb. The cross-section of the bristles orelements may be round, or elliptical, or rectangular, or wedge-shaped.

The invention provides in a second aspect a filtration barrier asdescribed in the first aspect comprising a first plurality of pairs ofbristles or elements wherein each pair of the first plurality comprisesa second bristle or element that is less stiff than a first bristle orelement. Each second bristle or element is lifted above each firstbristle or element when fluid flows backwardly between bristles orelements.

The invention provides in a third aspect a filtration barrier asdescribed in the first aspect comprising a second plurality of tripletsof bristles or elements. Each triplet of the second plurality comprisesa third bristle or element that is less stiff than a second bristle orelement, and a second bristle or element that is less stiff than thefirst bristle or element. Each third bristle or element is raisedfurther than each second bristle or element and each second bristle orelement is raised further than each first bristle or element when thefluid flows backwardly between the bristles or elements.

The invention provides in a fourth aspect a filtration barrier asdescribed in any prior aspect wherein variations of cross-sectionbetween individual bristles or elements determines stiffness.

The invention provides in a fifth aspect a filtration barrier asdescribed in any of the prior aspects wherein the free end of eachbristle or element extends in length beyond more than two said secondspaces, and wherein fluid flowing forwardly between adjacent singlesupport bars or strips passes sequentially through the first spaces ofmore than one comb.

The invention provides in a sixth aspect a filtration barrier asdescribed in any of the prior aspects wherein each comb in the pluralityof said combs is numbered 1, 2, 3, 4, etc., in a third sequence of combsto denote the position of each comb in the plurality, and wherein eachodd-numbered comb is a first comb and each even-numbered comb is asecond comb, and all the bristles or elements in each first comb branchfrom their single support bar or strip towards the right hand side, andall the bristles or elements in each second comb branch from theftsingle support bar or strip towards the left hand side.

The invention provides in a seventh aspect a filtration barrier asdescribed in any of the first, second, third, fourth, or fifth aspectswherein support joists are arranged in a parallel and equally-spacedapart array. The combs are assembled and fastened at an angle between 45and 135 degrees to the support joists in a fourth sequence of combs. Thebristles or elements of the next comb in the fourth sequence overlap thebristles or elements of one or more prior combs. In the fourth sequenceto form the filter barrier.

The invention provides in an eighth aspect a filtration barrier asdescribed in the sixth aspect wherein the support joists are arranged ina parallel and equally-spaced apart array, and whereon the combs areassembled and fastened at an angle between 45 and 135 degrees to thesupport joists in a fifth sequence of combs, wherein the bristles orelements of the next comb in the fifth sequence overlap the bristles orelements and the support bar or strip of one or more prior combs in thefifth sequence to form the filter barrier.

The invention provides in a ninth aspect a filtration barrier whosecomponents are defined in any of the first, second, third, fourth, orfifth aspects, wherein said bristles or elements are primary elementswithin a first sheet of resilient material, and the single bars orstrips are second elements within the first sheet. The primary elementsare arranged transversely to the second elements. The second elementsare in the same plane as the primary elements in their relaxed state.The primary elements are each anchored to the second elements at one endonly leaving a non-attached end free to be lifted out of said plane. Thesupport joists are narrow third elements that are attached to theunderside of the flat first sheet and are arranged at a common anglebetween 0 and 45 degrees to the second elements. The third elements arepositioned to prevent each said non-attached end moving past the thirdelements. The primary elements are grouped into pairs of primaryelements in a sequence of pairs wherein the second primary element ofeach pair less stiff than the first primary element. Each second primaryelement rises above each first primary element when fluid flowsbackwardly between the primary elements.

The invention provides in a tenth aspect a filtration barrier whosecomponents are those of the ninth aspect wherein the primary elementsare attached at each end to adjacent second elements, and wherein eachprimary element is of a flat and narrow zig-zag, or curved, orsinusoidal shape that increases its extensibility. The support joistsare narrow fifth elements that are attached to the underside of the flatfirst sheet and are arranged at a common angle between 45 and 135degrees to the primary elements, and wherein the fifth elements arepositioned below one or more places along the length of each primaryelement to prevent each primary element moving past the fifth elements.

The invention provides in an eleventh aspect a filtration barrier whosecomponents are those of either the ninth or tenth aspects wherein theprimary elements are grouped into triplets of primary elements in asixth sequence of triplets wherein the third primary element of eachtriplet is less stiff than the second primary element of each triplet,and the second primary element of each triplet within each sixthsequence is less stiff than the first primary element of each triplet.Each third primary element is raised further than each second primaryelement, and each second primary element is raised further than eachfirst primary element, when fluid flows backwardly between primaryelements.

The invention provides in a twelfth aspect a filtration barrier asdescribed in the eleventh aspect wherein the support joists are arrangedin a parallel and equally-spaced apart array. The combs are assembledand fastened with the support bars or strips positioned at an anglebetween 0 and 45 degrees to the support joists in a fifth sequence ofcombs. The bristles or elements of the next comb in the fifth sequenceoverlap the bristles or elements and the support bar or strip of one ormore prior combs in the fifth sequence to form the filter barrier.

The invention provides in a thirteenth aspect a filtration barrierwherein the bristles or elements of the first aspect become primaryelements within a first sheet of resilient material, and the single barsor strips of the first aspect become second elements within the firstsheet. The primary elements are arranged transversely to the secondelements, and the second elements share a common plane with the primaryelements in their relaxed state. The primary elements are each attachedto a second element at one end only leaving a non-attached end free tobe lifted out of the common plane. The support joists are narrow thirdelements attached to the underside of the flat first sheet and arearranged at a common angle between 0 and 45 degrees to the secondelements. The third elements are positioned to prevent each saidnon-attached end moving past the third elements. The primary elementsform pairs of primary elements in a sequence wherein the second primaryelement of each pair in the sequence is less stiff than the firstprimary element. Each second primary element is raised above each firstprimary element when the fluid flows backwardly between the primaryelements.

The invention provides in a fourteenth aspect a filtration barrier asdescribed in the thirteenth aspect wherein the primary elements areattached at each end to adjacent second elements, and each primaryelement is of a flat and narrow zig-zag, or curved, or sinusoidal shapethat increases its extensibility. The support joists are narrow fifthelements adjacent the underside of the flat first sheet and are arrangedat a common angle between 45 and 135 degrees to the primary elements.The fifth elements are positioned at one or more places along the lengthof each primary element to prevent each primary element moving past thefifth elements.

The invention provides in a fifteenth aspect a filtration barrier asdescribed in the thirteenth or fourteenth aspect wherein the primaryelements form triplets of primary elements in a sixth sequence oftriplets. The third primary element of each triplet is less stiff thanthe second primary element of each triplet, and the second primaryelement of each triplet is less stiff than the first primary element ofeach triplet. Each third primary element is raised further than eachsecond primary element and each second primary element is raised furtherthan each first primary element when the fluid flows backwardly betweenprimary elements.

The invention provides in a sixteenth aspect a filtration barrier asdescribed in the fifteenth aspect wherein a single first comb of thesixth aspect and a single second comb of the sixth aspect are overlappedand assembled as a paired ribbon. The single first comb and the singlesecond comb are appropriately spaced. The paired ribbon is wrappedaround a tubular grid as a helix wherein each successive wrap of thepaired ribbon appropriately overlaps a prior wrap to obtain the requiredspacing of first and second combs, whereby a tubular filter element isformed.

The invention provides in a seventeenth aspect a filtration barrierwherein the elements of the first aspect become warp elements within afilter mesh or screen. The single bars or strips of the first aspectbecome weft elements within the filter mesh or screen, wherein the warpelements are arranged transversely to the weft elements, and wherein thespaces between the warp elements are the filtration apertures. The weftelements and the warp elements lie in approximately the same plane intheir relaxed state. The warp elements are each secured to weft elementsat each end. The spaces between the weft elements are at least fourtimes the spaces between the warp elements. The support joists of thefirst aspect are stiff rod or wire elements that are adjacent to theunderside of the filter mesh or screen and are arranged at a commonangle between 0 and 45 degrees to the weft elements. The stiff rod orwire elements are spaced and positioned at intervals shorter than thespaces between the weft elements. The stiff rod or wire elements arespaced and positioned to limit the deflection of warp elements whenfluid flows forwardly past warp elements before passing between thestiff rod or wire elements. The warp elements are raised away from thestiff rod or wire elements when fluid flows backwardly between the warpelements. The warp elements are grouped into pairs of warp elements in asequence of the pairs wherein the first warp element of each pair in thesequence is more extensible than the second warp element. Each firstwarp element is raised above each second warp element when fluid flowsbackwardly between the warp elements.

The invention provides in an eighteenth aspect a filtration barrier asdescribed in the seventeenth aspect wherein the warp elements aregrouped into individual groups of warp elements in a sequence ofindividual groups. The first warp element of each individual group ismore extensible than the second warp element, the second warp element ofeach individual group is more extensible than the next warp element, andthereafter each next warp element of each individual group is moreextensible than the sequentially next warp element, until the last warpelement of each group is the least extensible warp element of eachindividual group. When fluid flows backwardly between the warp elementseach first warp element is raised above each second warp element of eachindividual group, and each second warp element is raised above each nextwarp element of each individual group, and thereafter each next warpelement of each individual group is raised above its sequentially nextwarp element, until the last warp element of each individual group isthe least raised warp element of each group.

The invention provides in a nineteenth aspect a filtration barrier asdescribed in the eighteenth aspect or nineteenth aspect whereinindividual warp elements comprise one or more filaments twisted togetherto form a rope or thread. Extensibility of individual warp elementsdecreases with an increase in the number of filaments in the individualwarp element.

The invention provides in a twentieth aspect a filtration barrier asdescribed in the seventeenth aspect or eighteenth aspect whereinindividual warp elements comprise a single fiber or filament.Extensibility of individual warp elements decreases as the cross sectionsize of the individual filament increases.

The invention provides in a twenty-first aspect a filtration barrier asdescribed in the seventeenth aspect or the eighteenth aspect whereineach warp element is of a zig-zag shape, or sinusoidal shape, or curvedshape.

In one or more embodiments, a filtration barrier of the presentinvention comprises a filter mesh. The filter mesh has a plurality ofgroups of flexible filter elements, with each group comprising at leasta first flexible filter element and a second flexible filter elementdisposed in spaced relation to the first flexible filter element. Withineach group, the first flexible filter element is more flexible than thesecond flexible filter element. The filter mesh further includes firstand second anchoring members spaced from each other. Each flexiblefilter element is secured to the first and second anchoring members andfree therebetween. A plurality of support members are disposeddownstream of the filter mesh for forward fluid flow through the filtermesh. The first and second flexible filter elements are configured suchthat the first and second flexible filter elements rest against one ormore of the support members during forward fluid flow through the filtermesh such that the first and second flexible filter elements aresupported against downstream deflection and lie in a common plane. Thecommon plane being transverse to a direction of forward fluid flowthrough the filter mesh. For each group, the first and second flexiblefilter elements are configured such that, in response to reverse fluidflow, opposite the direction of forward fluid flow, the first flexibleelement of that group displaces farther from the common plane than thesecond flexible filter element of that group displaces from the commonplane, such that a first backwash opening associated with the firstflexible element is larger than a second backwash opening associatedwith the second flexible element.

In one or more embodiments, a method of filtering includes providing afiltration barrier, forwardly passing fluid through a filter mesh of thefiltration barrier, and thereafter reversing fluid flow so that fluidflows through the filter mesh in a backwash direction. The filtrationbarrier includes a filter mesh and a plurality of support members. Thefilter mesh comprises a plurality of groups of flexible filter elements.Each group includes at least a first flexible filter element and asecond flexible filter element disposed in spaced relation to the firstflexible filter element. Within each group, the first flexible filterelement is more flexible than the second flexible filter element. Thefilter mesh further includes first and second anchoring members spacedfrom each other. Each flexible filter element is secured to the firstand second anchoring members and free therebetween. The plurality ofsupport members are disposed downstream of the filter mesh for forwardfluid flow through the filter mesh. During the forward fluid flow, foreach group, the first and second flexible filter elements rest againstone or more of the support members such that the first and secondflexible filter elements are supported against downstream deflection andlie in a common plane, the common plane being transverse to a directionof the forward fluid flow through the filter mesh. During the reversefluid flow, for each group, the first flexible element of that groupdisplaces farther from the common plane than the second flexible filterelement of that group displaces from the common plane, such that a firstbackwash opening associated with the first flexible element is largerthan a second backwash opening associated with the second flexibleelement.

The aspects described above can be employed to provide a continuouslyfiltering filter wherein a filtration barrier and a set of nozzles aremoved relatively to each other, and wherein flowing jets of washingfluid are directed backwardly onto the support joists side of thefiltration barrier to progressively flush a part, or parts of the filterbarrier, simultaneously fluid to be filtered is being driven forwardlythrough the remaining parts of the filtration barrier by a higher fluidpressure on the bristles or elements side of the filter barrier, therebyproviding washing fluid jets that locally and progressively lift thebristles or elements of a small part of the filtration barrier, therebyflushing ensnared particles from between or upon those bristles orelements, while filtration continues elsewhere, and wherein thedischarge direction of washing fluid exiting the bristles or elements ispreferably downwards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section of a filter comb.

FIG. 2 shows the filter comb of FIG. 1 with an additional stiffeningstrip supporting the bristles.

FIG. 3 shows a side view in cross section of part of a filtrationbarrier comprising filter combs of FIG. 1 or FIG. 4A in the filteringposition.

FIG. 4 shows a side view in cross section part of the filtration barrierof FIG. 3 with the bristles in the back-washing position.

FIG. 4A shows a part of the filter comb of FIG. 1 with the bristlesarranged as a sequence of triplets where each triplet comprises threebristles of decreasing width.

FIG. 5 shows the filter comb of FIG. 1 with the bristles inclined to theright.

FIG. 6 shows the filter comb of FIG. 1 with the bristles inclined to theleft.

FIG. 7 shows the filter comb of FIG. 1 with lengthened bristles.

FIG. 8 shows a side view in cross section of a section of a filtrationbarrier comprising several overlaying filter combs of FIG. 7 in thefiltering position.

FIG. 9 shows a plan view of a section of part of a filtration barriercomprising several filter combs of FIG. 1 or FIG. 4A or FIG. 7 in thefiltering position.

FIG. 10 shows a plan view of a section of part of the filtration barriercomprising several filter combs of FIGS. 5 and 6 laid in alternatelayers wherein the filter combs have lengthened bristles.

FIG. 11 is a schematic end view in cross section of a continuouslyfiltering filter where the filtration barrier is of tubular form.

FIG. 12 shows a plan view or part of the filtration barrier comprising ascreen with U-shaped slots with underlying support bars.

FIG. 13 shows an enlarged view of a section of the filtration barrier ofFIG. 12.

FIG. 14 shows a plan view of part of a filtration barrier comprising ascreen and support bars wherein zig-zagged flat elements of twoalternate widths are shown, and the elements are attached at one endonly.

FIG. 15 shows a plan view of part of the filtration barrier comprising ascreen and support bars wherein zig-zagged flat elements of twoalternate widths are shown, and the elements are attached at both ends.

FIG. 16 shows a plan view of part of filter screen or mesh with curvedand grouped warp elements arranged into groups wherein the warp elementsincrease in thickness and stiffness within each group.

DETAILED DESCRIPTION

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings.

FIG. 1 shows a section of a filter comb 10 wherein a plurality ofbristles or elements 11 are arranged parallel to each other and in acommon plane, and wherein each bristle or element branches from a singlestrip or bar or backbone 12.

FIG. 2 shows the filter comb of FIG. 1 with an additional stiffeningstrip 15 to assist holding the bristles or elements 11 in their parallelarrangement.

FIG. 3 is a side view in cross section of several filter combs 10, 10Aof FIG. 1 or 4A assembled into an array 18 wherein the single strip orbar of each filter comb is anchored onto transverse joists 13 with thefree end of each bristle or element 11 a, 11 b, and 11 c of each tripletof elements is supported upon the bristles and the single strips 12 ofthe next filter comb 10. The joists 13 are supported by transversebearers 14. The bristles 11 a, 11 b, and 11 c are shown in theirposition when the filtration barrier 10 or 10A is filtering and fluidflows downwards.

FIG. 4 is a side view in cross section the filter comb array 18 of FIG.3 with bristles or elements 11 a, 11 b, 11 c of each triplet of bristlesor elements shown in their open position when the filtration barrier 10is being back washed by an upwards flow of fluid through filtrationbarrier 10 and the free ends of bristles or elements are raised awayfrom the bristles of the next filter comb by the (back-wash) flow offluid from below.

FIG. 4 illustrates either the bristles 11 of FIG. 1 (shown by bristles11 a only), or the bristles 11 a, 11 b and 11 c of FIG. 4A arranged intriplets. Note that the most flexible bristle 11 c in each tripletdeflects furthest, the lesser flexible bristle 11 b in each tripletdeflects less far, and the least flexible bristle in each triplet 11 adeflects least.

FIG. 4A shows part of a single filter comb 10A, similar to that of FIG.1, with sequenced triplets of bristles 11 a, 11 b, 11 c, with eachbristle lengthened and branching from a single strip or backbone 12,wherein the bristle 11 c in each triplet is narrower than the adjacentbristle 11 b, and the bristle 11 b in each triplet is narrower than theadjacent bristle 11 a. FIG. 5 shows a filter comb 20, similar to that ofFIG. 1 with its bristles 11 inclined to the right, and branching from asingle strip or bar or backbone 12.

FIG. 6 shows a filter comb 20A1 similar to that of FIG. 1 with itsbristles 11 inclined to the left, and branching from a single strip orbar or backbone 12.

FIG. 7 shows a single filter comb 30, similar to that of FIG. 1 withbristles 31 considerably lengthened and branching from a single strip orbackbone 32.

FIG. 8 is a side view in cross section of several filter combs 30 ofFIG. 7 assembled into a filter barrier 40 wherein the bristles of eachfilter comb is anchored onto joists 33 with the free end of each bristlesupported upon the bristles of underlying filter combs. The joists 13are themselves supported by bearers (not shown) like the bearers 14 ofFIG. 3. The bristles or elements are shown in their position when thefiltration barrier 40 is filtering: in this example, fluid passesthrough nine layers of bristles. Items common to FIG. 7 are shown bylike numbers.

FIG. 9 shows a plan view of a part of a filtration barrier 50 comprisinga plurality of the 30 filter combs of FIG. 7 or FIG. 4A. It is a view aswould be seen from above the array of FIG. 8. The dimension Y shows thelength of the bristles in one comb. Items common to FIG. 7 are shown bylike numbers.

FIG. 10 shows a plan view of a part of the filtration barrier 60comprising several filter combs of FIGS. 5 and 6 laid in overlappingalternate layers wherein the filter combs have lengthened bristles. Thedimension Z shows the length of the bristles in one comb. Items commonto FIGS. 5 and 6 are shown by like numbers.

FIG. 11 is a schematic end view in cross section of a continuouslyfiltering filter 70 wherein the filtration barrier is of tubular form.It shows a filtration barrier 71 wherein a rotating set of filtercleaning nozzles 74 deliver streams of back-washing fluid onto theinside of the filtration barrier 71, and the rotating set of filtercleaning nozzles are carried on a hollow arm 73, which is attached to acentral driven hollow shaft 72, which moves the cleaning nozzlesprogressively and continuously around inside the filtration barrier tolocally lift and flush the bristles of the filtration barrier whilefiltration continues in all other parts of the filter barrier.Filtration is continued by the filter 70 being immersed in a fluidcontaining particles to be filtered with the pressure within the insidespace 75 being at a lesser pressure than that outside of the filterbarrier 70. The preferred orientation is with the axis vertical,allowing particles 76 flushed from the filtration barrier to fall awayfrom the filter and collect at its base.

FIG. 12 shows a section of a filtration barrier 80 that comprises ascreen 82.

FIG. 13 shows an enlargement of the designated “Section A” of thefiltration barrier 80 shown in FIG. 12 wherein un-perforated regions ofthe screen 82 are shown shaded and the support joists 83 and supportbearers 81 (supporting the joists 83) are shown as dotted lines toindicate that they lie under the screen 82. The screen 82 is aperforated thin sheet (of metal or an appropriate plastic) withresilient properties perforated with a plurality of U-shaped slots 84.In this example each of the U-shaped perforations 84 have a cantileveredcentral strip 85 that is attached to (or continuous with) the thin sheetat one end: it is thereby free to deflect resiliently as a cantileveraway from the plane of the thin sheet thereby increasing the flow areafor fluid flowing through the slot. When fluid flows forwardly (throughthe screen before flowing through the support bars 81 and 83) thecentral strip 85 is supported by the support bars 83 and deflection ofthe central strip 85 is thereby restricted when fluid flows forwardlythrough the apertures towards the support bars 83. When fluid flowsbackwardly through the screen 80 each strip 85 is unsupported, and eachstrip can yield resiliently increasing the flow area through the U-slotsto more easily release particles that have been entrapped within theU-slots. The resilience of each strip 85 causes it to return to thesupported position shown in FIG. 13 whenever the flow through the screenflows forwardly again.

Although the slots 84 in this example are shown as generally rectangularin shape, they are not limited to this shape. Slots that are part-round,or part-square, or part elliptical, or curved, with strips 85 that arezig-zag shaped with square or rounded corners can be readily devised,and the outer contour of the slots 84 surrounding each strip 85 can beshaped to provide a variety of different slot or hole shapes.

FIG. 14 shows a section of a filtration barrier 100 that comprises ascreen 102 wherein there are several strips 101A and 101B that arezig-zag in shape (to confer greater extensibility) with slots betweeneach strip 101A and 101B, wherein the strips 101A are narrower (andthereby more flexible) than the strips 101B. The strips 101A and 101Bare attached to the sheet 102 at one end only. The support bars 103support the free ends of strips 101A and 101B against deflection whenfluid flows forwardly through the apertures towards the support bars103. When deflection due to fluid flowing backwardly through the slotsoccurs the narrower strips 101A deflect more than strips 101B to provideincreased flow areas through the slots.

FIG. 15 shows a section of a filtration barrier 90 that is similar tothat of FIG. 14 wherein the strips 91A and 91B are attached to sheet 92at both ends. The support bars 93 support the central region(s) ofstrips 91A and 91B against deflection when fluid flows forwardly throughthe slots towards the support bars 93. When deflection due to fluidflowing backwardly through the slots occurs the narrower strips 91Bdeflect more than strips 91A to provide increased flow areas through theslots.

FIG. 16 shows a plan view of part of a filter screen or mesh 110 withcurved and grouped warp elements 111 a,111 b,111 c and 111 d, which arearranged into groups, with each group comprising four warp elements, andwhere within each group warp elements 111 a are thinner (and therebymore flexible) than warp elements 111 b, and warp elements 111 b arethinner (and thereby more flexible) than warp elements 111 c, and warpelements 111 c are thinner (and thereby more flexible) than warpelements 111 d. Weft elements 112 secure the ends of all the warpelements at intervals, and support joists 113 underlay the warp elementsat intervals between adjacent weft elements and support the warpelements when fluid being filtered flows downwards (or forwardly) pastwarp elements before flowing past the support joists 113. Support joists113 are supported by bearers 114, which either lie under the joists 113or are cross members of a grid containing both joists 113 and bearers114. When fluid flows upwards (or backwardly) support joists 113 nolonger support warp elements, whereby warp elements 111 a deflectupwards more than warp elements 111 b, and warp elements 111 b deflectupwards more than warp elements 111 c, and warp elements 111 c deflectupwards more than warp elements 111 d, thereby progressively increasingflow area through the filter screen or mesh 110.

It will be appreciated by persons skilled in the art that numerousvariations end/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and features of any embodiment may be adapted, or extendedinto other embodiments.

What is claimed is:
 1. A filtration barrier, comprising: a filter meshcomprising: a plurality of groups of flexible filter elements; eachgroup comprising a first flexible filter element and a second flexiblefilter element disposed in spaced relation to the first flexible filterelement; first and second anchoring members spaced from each other,wherein each first and second flexible filter element of each of theplurality of groups is secured to both the first and second anchoringmembers and free therebetween; wherein, within each group, the firstflexible filter element is more flexible than the second flexible filterelement; a plurality of support members disposed downstream of thefilter mesh for forward fluid flow through the filter mesh; wherein thefirst and second flexible filter elements are disposed so as to restagainst one or more of the support members during forward fluid flowthrough the filter mesh such that the first and second flexible filterelements are supported against downstream deflection and lie in a commonplane, the common plane being transverse to a direction of forward fluidflow through the filter mesh; wherein, for each group, the first andsecond flexible filter elements are configured such that, in response toreverse fluid flow, opposite the direction of forward fluid flow, thefirst flexible element of that group displaces farther from the commonplane than the second flexible filter element of that group displacesfrom the common plane, such that a first backwash opening associatedwith the first flexible element is larger than a second backwash openingassociated with the second flexible element.
 2. The filtration barrierof claim 1: wherein each group further comprises a third flexible filterelement, the second flexible filter element being more flexible than thethird flexible filter element; wherein, for each group, the second andthird flexible filter elements are configured such that, in response toreverse fluid flow, the second flexible element of that group displacesfarther from the common plane than the third flexible filter element ofthat group displaces from the common plane, such that a third backwashopening associated with the third flexible element is smaller than thesecond backwash opening.
 3. The filtration barrier of claim 2: whereineach group further comprises a fourth flexible filter element, the thirdflexible filter element being more flexible than the fourth flexiblefilter element; wherein, for each group, the third and fourth flexiblefilter elements are configured such that, in response to reverse fluidflow, the third flexible element of that group displaces farther fromthe common plane than the fourth flexible filter element of that groupdisplaces from the common plane, such that a fourth backwash openingassociated with the fourth flexible element is smaller than the thirdbackwash opening.
 4. The filtration barrier of claim 1, wherein theanchor members are disposed orthogonal to the first and second flexiblefilter elements.
 5. The filtration barrier of claim 1, wherein theflexible filter elements are disposed in a regular pattern such that, inresponse to forward fluid flow through the filtration barrier, filterapertures between adjacent flexible filter elements are substantiallythe same size.
 6. The filtration barrier of claim 1, wherein the firstand second flexible filter elements have a round cross-section.
 7. Thefiltration barrier of claim 1, wherein the first and second flexibleelements are formed from identical materials, but have differentcross-sectional profiles.
 8. The filtration barrier of claim 1, whereinthe first and second flexible elements have different materialproperties, but identical cross-sectional profiles.
 9. The filtrationbarrier of claim 1, wherein the first and second flexible elements haveboth different material properties and different cross-sectionalprofiles.
 10. The filtration barrier of claim 1, further comprisingjoists supporting the support members.
 11. A method of filtering,comprising: providing a filtration barrier, the filtration barriercomprising: a filter mesh comprising: a plurality of groups of flexiblefilter elements; each group comprising a first flexible filter elementand a second flexible filter element disposed in spaced relation to thefirst flexible filter element; wherein, within each group, the firstflexible filter element is more flexible than the second flexible filterelement; first and second anchoring members spaced from each other,wherein each first and second flexible filter element of each of theplurality of groups is secured to both the first and second anchoringmembers and free therebetween; a plurality of support members disposeddownstream of the filter mesh for forward fluid flow through the filtermesh; forwardly passing fluid through the filter mesh, wherein duringthe forward fluid flow: for each group, the first and second flexiblefilter elements rest against one or more of the support members suchthat the first and second flexible filter elements are supported againstdownstream deflection and lie in a common plane, the common plane beingtransverse to a direction of the forward fluid flow through the filtermesh; thereafter, reversing fluid flow so that fluid flows through thefilter mesh in a backwash direction, opposite to the direction offorward fluid flow; wherein, during the reverse fluid flow: for eachgroup, the first flexible element of that group displaces farther fromthe common plane than the second flexible filter element of that groupdisplaces from the common plane, such that a first backwash openingassociated with the first flexible element is larger than a secondbackwash opening associated with the second flexible element.
 12. Themethod of claim 11: wherein each group further comprises a thirdflexible filter element that is less flexible than the second flexiblefilter element; wherein during the forward fluid flow, for each group,the third flexible filter element rests against one or more of thesupport members such that the third flexible filter element is supportedagainst downstream deflection and lies in the common plane; wherein,during the reverse fluid flow, for each group, the second flexibleelement of that group displaces farther from the common plane than thethird flexible filter element of that group displaces from the commonplane, such that the second backwash opening associated with the secondflexible element is larger than a third backwash opening associated withthe third flexible element.
 13. The method of claim 12: wherein eachgroup further comprises a fourth flexible filter element that is lessflexible than the third flexible filter element; wherein during theforward fluid flow, for each group, the fourth flexible filter elementrests against one or more of the support members such that the fourthflexible filter element is supported against downstream deflection andlies in the common plane; wherein, during the reverse fluid flow, foreach group, the third flexible element of that group displaces fartherfrom the common plane than the fourth flexible filter element of thatgroup displaces from the common plane, such that the third backwashopening associated with the third flexible element is larger than afourth backwash opening associated with the fourth flexible element. 14.The method of claim 11, wherein the anchor members are disposedorthogonal to the first and second flexible filter elements.
 15. Themethod of claim 11, wherein the flexible filter elements are disposed ina regular pattern such that, during the forward fluid flow, filterapertures between adjacent flexible filter elements are substantiallythe same size.
 16. The method of claim 11, wherein the first and secondflexible filter elements have a round cross-section.
 17. The method ofclaim 11, wherein the first and second flexible elements are formed fromidentical materials, but have different cross-sectional profiles.